Oncogenes have, in many cases, been shown to interfere with as well as growth regulation. Very little is known, however, about differentiation the relationship between these oncogene functions. The goal of the proposed project is to determine the mechanism of SV40 large T antigen in a well defined, novel assay for differentiation. In order to determine, at a molecular level, how T antigen blocks differentiation we will perform the following experiments: 1. A detailed structure-function analysis of SV40 T antigen block of adipocyte differentiation using existing mutants. 2. Determine whether Sv40 T antigen blocks adipocyte by differentiation interfering with growth factor regulated cell cycle arrest. 3. Determine how SV40 T antigen suppresses the expression of an adipocyte-specific gene family.